In general, an embedded system may be described as a special purpose computing system designed to perform one or a few dedicated functions. Embedded systems are commonly used in consumer devices like personal digital assistants, mobile phones, videogame consoles, microwaves, washing machines, alarm systems, and digital cameras. In addition to the consumer space, embedded systems are used in nearly every industry, from telecommunications to manufacturing, and from transportation to medical devices. In fact, embedded systems are so commonly in use today that it is not feasible to exhaustively list specific examples.
The term “embedded system” does not have a precise definition, and determining what is and is not an embedded system can be difficult. For example, a general purpose computer, such as a laptop, is not typically characterized as an embedded system. However, a laptop is usually composed of a multitude of subsystems such as the hard disk drive, the motherboard, the optical drive, the video processing unit, and various communication devices. Many of the individual subsystems comprising the laptop may themselves be embedded systems.
The complexity of embedded systems can vary from, for example, systems with a single microcontroller chip and a light emitting diode to systems with multiple microprocessor units and various peripheral communication interfaces and mechanical parts. Manufacturers of modern microprocessors are increasingly adding components and peripheral modules to their microprocessors, creating what may be thought of as embedded processors. This type of embedded system is often referred to as a system on a chip (SoC). A simple example of a system on chip is an application-specific integrated circuit (ASIC) packaged with a universal serial bus (USB) port. Additionally, embedded systems range from those having no user interface at all to those with full user interfaces similar to a desktop operating system.
There are many advantages to using embedded systems. For example, an embedded system typically is designed to do some specific task, as opposed to being a general purpose computer with a wide range of features for performing many different tasks. As a result, design engineers can optimize the embedded system for the desired task, which assists in reducing the size and cost of the device as well as increasing its reliability and performance. Furthermore, functionalities can be designed into an embedded system that would not be feasible using hardware alone.
The software that operates an embedded system is generally referred to as “firmware.” Firmware is often stored on read only memory (“ROM”) based storage devices. For example, flash-based read only memory or electronically erasable read only memory (“EEPROM”) devices are often used to store firmware. The firmware is used to control the various features, functioning, and interfaces of the embedded system. Thus, a digital video disk player will have firmware that processes the appropriate response to an input, such as the user pressing the “power” button or the “play” button. Additionally, the firmware in this example would control the storage mechanism, the digital processing circuitry used to decode and output onto the appropriate ports the video and audio signals stored on the video storage medium, as well as the user interface allowing the user to configure settings of the digital video disk player.
Many embedded systems include among their hardware components a processing unit, which is capable of executing software instructions stored on a computer-readable medium. As those of skill in the art will appreciate, some of these processing units are capable of dynamically scaling their frequency or voltage settings or both. This capability is commonly referred to as dynamic voltage and frequency scaling (DVFS). Dynamic voltage and frequency scaling is typically implemented to achieve certain efficiencies, such as, for example, lower power consumption and lower heat generation.
Most modern processing units include the ability to synchronize the frequency and voltage transitions within the processing unit itself. However, various other hardware components that share a data bus that has its frequency change may require synchronization. Additionally, hardware components that share a voltage rail which has its voltage change may also require synchronization.